I would say an amp is essential. Playing too hard so as to be heard acoustically sets up all sorts of wrong precedents. A very small mixer so you can put two basses + music through said amp makes everything tidy. When I used to teach, certainly with beginners, I would ask them what song they wanted to play. Obv, sometimes there was a bit of direction needed. But if it is their song then there is a huge amount of determination to make it right. Tricky passages can be simplified so that they get the full experience. I also did one octave 24/124/134 scales with alternate fingers on the right hand so that they begin to develop dexterity right from the start. Obviously, 1 finger was enough for Jamerson should be enough for us, but.......